The dispersal of automotive lead from metropolitan Adelaide into adjacent rural areas

Abstract

About 600 surface samples and key horizons of 240 soil profiles from a 90 x 20 km study area extending from the metropolitan area of Adelaide, South Australia, to its rural hinterland, were analysed for lead. Atmospheric fallout was collected monthly at 19 locations for 2 years, and up to 3 years at fewer sites in the same area. Lead in atmospheric fallout showed little year-to-year variation and tended to be seasonally controlled with highest values in winter. Collection of lead in fallout was unaffected by the filtering action of vegetation. The lead content of surface soils and atmospheric fallout showed that part of petrol-lead emitted within Adelaide from automotive exhausts has measurably contaminated the rural landscape to about 50 km downwind of the city. The variation in lead content of surface soils in the agricultural region near Adelaide can be largely explained in terms of accessions of aerosol-lead of automotive origin. This research complements previous investigations which showed that the lead isotopic compositions of selected soils were close to the composition of the lead tetraethyl used in South Australia. An environmental budget showed that only 3% of the lead in petrol burned in Adelaide has been dispersed via the atmosphere beyond the immediate highway zone, and deposited on the land surface within 50 km of the city centre. On the assumption that no more than 35% of the lead is retained within the vehicle, and that about half of the total burned lead is deposited near the roadway, the 30% of the total lead which cannot be accounted for (about 200 t at the time of this study) has probably dispersed beyond the study region and should be viewed as a contribution to continental and global pollution. Lead levels measured in rainfall, air and soils were low in relation to the accepted standards and experience. Although the lead levels were low, this investigation indicates the likely dispersal pattern of other pollutants with similar atmospheric residence times, and thus provides guidance to planning decisions concerning placement of polluting industries, and in relation to possible industrial accidents which cause pollution.